1. Field of the Invention
The present invention relates to a reactor for anaerobic purification of waste water, particularly waste water from the paper industry, including a reactor vessel that has at least one inlet for supplying waste water to be purified into the reactor, at least one outlet for discharging purified water, at least one sediment drain and at least two multi-phase separator devices arranged on top of one another.
2. Description of the Related Art
A multitude of mechanical, chemical and biological methods and corresponding reactors are known for purification of waste water. In biological waste water purification, the waste water to be purified is brought into contact with aerobic or anaerobic micro-organisms which, in the case of aerobic micro-organisms decompose organic contaminants contained in the waste water predominantly to carbon dioxide, biomass and water, and in the case of anaerobic micro-organisms mainly to carbon dioxide and methane and only in small part to biomass.
In recent times the biological waste water purification methods are hereby carried out increasingly with anaerobic micro-organisms, since with the anaerobic waste water purification oxygen does not have to be supplied into the bioreactor at a high energy expenditure; energy-rich biogas is produced during purification which can subsequently be utilized for generating energy; and substantially lower volumes of excess sludge are produced.
Depending on the type and form of the utilized biomass, the reactors for anaerobic waste water purification are categorized into contact sludge reactors, UASB-reactors, EGSB-reactors, fixed bed reactors and fluidized bed reactors.
Whereas the micro-organisms in fixed bed reactors adhere to stationary carrier materials and the micro-organisms in fluidized bed reactors adhere to freely moving, small carrier material; the micro-organisms in UASB and EGSB reactors are utilized in the form of so-called pellets. In contrast to UASB (upflow anaerobic sludge bed) reactors, EGSB (expanded granular sludge bed) reactors are higher and at the same volume have a substantially smaller base surface.
In the case of UASB and EGSB reactors, waste water which is to be purified, or a mixture of waste water which is to be purified and already purified waste water from the outlet of the anaerobic reactor is fed continuously to the reactor through an inlet which is arranged in the lower region of the reactor and is directed through a micro-organism pellet-containing sludge bed which is located above the inlet.
During decomposition of the organic compounds from the waste water, the micro-organisms form in particular methane and carbon dioxide containing gas (which is also referred to as biogas) which partially adheres to the micro-organism pellets in the form of small bubbles and which partially rises to the top in the reactor in the form of free gas bubbles. Because of the added gas bubbles the specific weight of the pellets decreases, which is the reason that the pellets rise to the top in the reactor. In order to separate the formed biogas and the rising pellets from the water, separators are arranged in the center and/or upper part of the reactor, mostly in the embodiment of gas hoods under the top of which biogas accumulates, forming a gas cushion, under which a flotation layer consisting of micro-organism pellets and waste water is disposed. Purified water, relieved of gas and micro-organism pellets rises upwards in the reactor and is drawn off at the upper end of the reactor through overflows. Methods of this type and associated reactors are described for example from EP 0 170 332 A and EP 1 071 636 B.
In heavy duty reactors for anaerobic waste water treatment normally 2 three-phase separator devices are used. These consist of gas collector hoods which are arranged offset on top of one another, beneath which rising biogas bubbles and rising granular bio-sludge (pellets) accumulates. As already mentioned, the gas is removed from the hoods. The granulated biomass either eliminates gas adhering to it and sinks then again to the reactor bottom or is transported in the form of a gas/water/pellet mixture through a pipe system in a gas separator device on the reactor head where it is subjected to shearing forces. Due to this the gas separates from the biomass, and the granular sludge is returned into the process. The upper three-phase separator device normally also forms the roof of the reactors.
What is needed in the art is to improve the capacity of the reactor with as little effort as possible.